Basically, except as noted below, we agree. As usual, I discussed the
thread topic 'leaning in the direction' of the work I've done -
trying yet another way to enable folks to see it's stuff.
"r norman" <rsnorman_ at _comcast.net> wrote in message
news:kqe3avolhembfp64ld5jj9fnjq42b60t46 at 4ax.com...
| Note: my comments are all at the end
|| On Sat, 19 Apr 2003 19:26:26 GMT, "KP-PC"
| <k.p.collins at worldnet.att.net%remove%> wrote:
|| >I'll Appreciate your discussion, Richard.
| >
| >"r norman" <rsnorman_ at _comcast.net> wrote in message
| >news:gtv2av0l7fo5opblku4n3lbteof7f6pa2l at 4ax.com...| >| On 18 Apr 2003 20:26:19 -0700, y.k.y at lycos.com (yan king yin)
| >wrote:
| >|
| >| >Inside the brain there are ubiquitous fluctuations of
| >| >electric fields of magnitude ~100mV, due to nerve impulses.
| >| >Most of the standard connectionist models of the brain
| >| >do not take this effect into account. Is this some noise
| >| >that can be ignored?
| >| >
| >| >I think one way to know the extent of the significance
| >| >of this E field is to induce some random ~100mV E fields
| >| >externally from the scalp, and see if they wreck the
| >| >mind =)
| >| >
| >| >Can anyone point me to some references or facts...
| >| >
| >| >Thanks,
| >| >YKY
| >| >
| >| >P.S. Personally I know of 2 instances. One is the
| >| >"ephatic coupling" of parallel nerve fibers that tends
| >| >to synchronize nerve impulses. Second is the effect of
| >| >E fields on growth cone dynamics. Both of these theories
| >| >are not very mainstream it seems.
| >|
| >| There are fields and there are fields.
| >|
| >| The 100 mV potentials you describe are specifically across the
| >| cell membrane. If you want to talk about electric fields, 100
mV
| >| across a 100 A membrane (10 nm) gives a field strength of some
| >| 10,000,000 V/m. It takes a pretty decent dielectric to hold up
| >| against that!
| >|
| >| However, these potentials are in specific locations caused by
| >| sources that have the proper impedance characteristics (channel
| >| conductances) to produce the necessary current. Most of the
brain,
| >or
| >| any organ of the body for that matter, is salt water with a very
| >high
| >| conductance. The electric fields in either the intracellular or
| >the
| >| extracellular spaces are very small. It is very hard to induce
| >| potentials in these media from externally applied fields because
of
| >| the high conductance.
| >|
| >| It is, in fact, the high conductance of the extracellular medium
| >that
| >| makes ephatic interaction between nerve cells so ineffective.
Only
| >if
| >| the adjacent cells are extremely close and only if there is some
| >| special confinement of extracellular space (as, for example,
| >wrapping
| >| by a common glial cell) can current densities reach a high
enough
| >| level to produce an electrical potential that significantly
alters
| >| cell function.
| >
| >I disagree. During the course of long-term 'focused' neural
| >activation [as is the case in devoted problem-solving activity]
| >conductance gradients build because, for instance, glia act as K+
| >electrodes which instantiates K+ distribution, which alters
'resting
| >potentials', which alters action potential energydynamics - which
| >results in altered nervous system function that's traceable back
to
| >ionic conductances.
| >
| >| Growth cones are influenced by electric fields. You can produce
a
| >| strong enough field with special experimental chambers and
| >electrodes.
| >| It is difficult to produce that strong a field with external
| >| radiation. People routinely work in areas of very high electric
| >field
| >| intensity without any hint of mind altering events.
| >
| >The fact that, if 'memory' is to occur, one thing that =must=
occur
| >is that 'growth cones' =must= exhibit trophic dynamics having
| >specific correlation to the neural activation that actually does
| >occur within a nervous system, points directly to a necessary
| >coupling to the net energydynamics inherent.
| >
| >Yes, there are 'molecular' dynamics involved, but as I've
discussed
| >in other threads, these, too, =must= be rigorously-coupled to the
| >energydynamics inherent in the activation that actually occurs
within
| >the nervous system, else the molecular dynamics would be
| >'superfluous' with respect to 'memory' and 'learning', and
therefore,
| >'without consequence'. But why would evolutionary dynamics leave
=so
| >much= supposedly 'inconsequential' stuff within nervous systems,
all
| >of it consuming energy that's only be going to Waste?
| >
| >The 'point' I'm discussing is at the most-Fundamental 'level' of
| >nervous system function - but it's 'where' everything is
| >tied-together ['where' everything within the nervous system
becomes
| >rigorously coupled, not only with respect to it's various
| >'components' and processes, but with respect to energydynamics
| >external to the nervous system.
| >
| >In other words, if external physical reality is to be 'known',
then
| >the internal energydynamics have to be coupled to the external
| >energydynamics 'all the way down'. ["It's activation dependence
all
| >the way down, not turtles." :-]
| >
| >With respect to your thoughtful discussion of conductances, a
factor
| >you left out is the that the 3-D neural Topology, itself, greatly
| >restricts energy's freedom to move within a nervous system - co
| >'conductance' doesn't occur as a 'blob'. It occurs in the
| >highly-restricted way that's Determined by the 3-D neural
| >architecture. Relatively-repetitive 'pumping' within
| >activation-defined regions of the 3-D neural Topology [as occurs
with
| >respect to 'focussed' neural activation] results in
| >increasingly-restricted energy's freedom to move. Then, all
| >'learning' has to do is 'follow' the energy-gradient inherent, and
| >undergo trophic dynamics that rigorously reflect such.
| >
| >It's not a 'blob'. Conductances are not 'willy-nilly', but
| >extremely-restricted by the fact of the 3-D neural architecture's
| >existence.
| >
| >I'll Appreciate your comments.
| >
| >Cheers, Richard, ken [K. P. Collins]
| >
| You make two points.
|| First: about glial cells. Yes, they can influence nerve activity
| through their metabolic activities and by afffecting the ion
| concentration in the extracellular space. But the original query
was
| about electric fields. The effects you mention do not work via
that
| mechanism.
I thought my discussion was clear enough with respect to such, but it
doesn't matter. I was actually taking the opportunity to discuss
normal in vivo energydynamics.
| Second: about 3D neural topology. Yes, of course the nervous
system
| is highly organized and is most definitely not a "blob". However,
the
| organization is cellular and the structures are separated by cell
| membranes. These have a time constant on the order of, say, 10
msec.
| Therefore, for AC electric fields with frequency larger than 2
pi/tau
| or about16 Hz, the boundaries between cells don't really matter.
| Especially for frequencies high enough to be effectively radiated,
the
| brain is for all intents and purposes a bowl of salt water mush.
| Again, my only concern in my post is with electric field effects.
| Basically, what I was arguing is that, although there are electric
| fields in the brain, "electric field effects"per se really aren't
very
| significant in the way that nerve cells function.
|| You have a third point about the significance of energy dynamics
| which, frankly, I don't follow especially since I haven't been
| following your numerous posts. But again, if whatever it is you
mean,
| it is not electric fields and so is not relevant to the original
| query.
I was actually taking the opportunity to discuss normal in vivo
energydynamics.
I was discussing why relatively-uniform fields don't 'address'
information-content within nervous systems, which was my way of
addressing the stuff of the original question.
I'm 'desperate' with wanting to get the =general= 3-D energydynamics
point across.
ken